Move to libadwaita for preferences window
We want to simplify our preferences story (they still need to be dynamic, but we can drop libdazzle usage).
- Use AdwPreferencesWindow and similar for preferences
- Add symbolic icons for groups in the sidebar
- Remove use of multiple columns (DzlColumnView) which would happen naturally with AdwPreferencesWindow
- Look at rearranging where some settings are placed, in particular language stuff will need simplification